<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <div id="app">
        {{ date }}
    </div>
    <script src="https://unpkg.com/vue/dist/vue.min.js"></script>
    <script>
        var app = new Vue({
            el: '#app',
            data: {
                date: new Date()
            },
            mounted: function () {
                var _this = this;
                this.timer = setInterval(function () {
                    _this.date = new Date();
                }, 1000);
            },
            beforeDestroy: function () {
                if (this.timer) {
                    clearInterval(this.timer);
                }
            }
        })
    </script>
</body>
</html>